STM32: Add sound support using DAC

[danielinux]

• [x] Initialize and configure DAC
• [x] write driver for /dev/dsp
• [ ] enable sound FX in DOOM

Looks like a nice (POSIX) interface to implement could be OSS http://manuals.opensound.com/developer/

[danielinux]

IOCTL required for DOOM:

• [ ] SNDCTL_DSP_SETFRAGMENT
• [ ] SNDCTL_DSP_RESET
• [ ] SNDCTL_DSP_STEREO
• [ ] SNDCTL_DSP_GETFMTS
• [ ] SNDCTL_DSP_SETFMT
• [ ] SNDCTL_DSP_SPEED

[danielinux]

http://www.st.com/content/ccc/resource/technical/document/application_note/05/fb/41/91/39/02/4d/1e/CD00259245.pdf/files/CD00259245.pdf/jcr:content/translations/en.CD00259245.pdf

[danielinux]

Simple DAC driver working. I2S drivers will be tracked in other issues.